Device for balancing an arm pivoting about an axis of rotation, for example, an arm supporting a work station all-purpose fume or gas exhaust conduit

ABSTRACT

The torque, due to the weight of the arm, is balanced according to the angular position of the arm by a contrast spring acting perpendicular to the axis of rotation of the arm. The spring is controlled by a cam integral with the arm, is housed in a container closed by a wall acted on by the profile of the cam, and rests on a guide disk whose position relative to the container is adjusted by means of an adjusting screw to calibrate the precompression of the spring according to the minimum torque due to the weight of the arm. In another embodiment, at least one contrast spring acts parallel to the axis of rotation of the arm, and is controlled by a cam edge of a cylinder for axially moving a corresponding sleeve housing the spring.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the 371 National Phase of International ApplicationNo. PCT/IT03/00318, filed May 23, 2003, which was published in Englishunder PCT Article 21(2) as International Publication No. WO 03/100313,which claims priority of Italian Application No. TO2002 A000437, filedMay 23, 2002. Each aforementioned application is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention relates to a device for balancing an arm pivotingabout an axis of rotation, for example, an arm supporting a work stationall-purpose fume or gas exhaust conduit.

BACKGROUND ART

In an arm pivoting about an axis of rotation, the torque, with respectto the axis of rotation, due to the weight of the arm and any fixturesupported by it, often varies alongside the angular position of the armabout the axis. The arm can be used for various types of equipment,particularly those involving moving the fixture by manually rotating thearm.

To reduce the effort required of the user, the torque due to the weightof the arm is normally balanced by elastic means, such as a contrastspring; and, to compensate the variation in torque produced by avariation in the angular position of the arm, means have been proposedfor automatically controlling the action of the spring according to theangular position of the arm.

In an all-purpose fume exhaust conduit, an arm balancing device has beenproposed in which the action of the spring is regulated by means fittedto an articulated parallelogram, the pivot of which is eccentric withrespect to the axis of rotation of the arm. Though satisfactory in termsof performance, the above balancing device is relatively complex andexpensive to produce, on account of the large number of moving parts,and the rods of the parallelogram having to be formed to house thespring inside a substantially closed channel.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a highly reliable,low-cost device for balancing an arm pivoting about an axis of rotation,and designed to eliminate the aforementioned drawbacks of knownbalancing devices.

According to the present invention, there is provided a device forbalancing an arm pivoting about an axis of rotation, and so located asto vary the torque, due to the weight of said arm and with respect tosaid axis of rotation, according to the angular position of said arm;said torque being balanced by the contrasting action of elastic means;and control means being provided to control said contrasting actionaccording to said angular position; characterized in that said controlmeans comprise at least one cam member associated with said arm andwhich acts on said elastic means to control said contrasting action.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of preferred, non-limiting embodiments of the invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 shows a view in perspective of a work station all-purpose fume orgas exhaust conduit featuring two pivoting arms fitted with respectivebalancing devices in accordance with a first embodiment of theinvention;

FIG. 2 shows a larger-scale, partial exploded view in perspective of thetwo arms and respective balancing devices in FIG. 1;

FIG. 3 shows a side view of a detail in FIG. 2;

FIG. 4 shows a view in perspective of the FIG. 1 conduit featuring armsfitted with balancing devices in accordance with a further embodiment ofthe invention;

FIG. 5 shows a larger-scale, exploded view in perspective of one of theFIG. 4 balancing devices;

FIG. 6 shows a detail of the FIG. 5 device;

FIG. 7 shows an exploded view in perspective of another of the FIG. 4balancing devices;

FIG. 8 shows a detail of the FIG. 7 device;

FIG. 9 shows an exploded view in perspective of a variation of FIG. 5balancing device;

FIG. 10 shows a detail of the FIG. 9 device.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 5 in FIG. 1 indicates as a whole an all-purpose fume or gasexhaust conduit, e.g. for a work station in a factory or workshop.Conduit 5 preferably has a circular cross section, is fitted at one endwith an exhaust hood 6 moved manually over to the fume source, and isdefined by two straight portions 7 and 8 connected to each other by aflexible articulated connecting portion 9. Portions 7 and 8 are alsoconnected by another two articulated connected portions 11 and 12 to arigid portion 13 of conduit 5 and to hood 6 respectively.

Rigid portion 13 rotates inside a sleeve having a flange 10 connectingthe sleeve to a fixed support 14 possibly housing an aspirator notshown. More specifically, conduit 5 is defined by a single flexible,e.g. undulated, pipe, the two portions 7 and 8 of which are fixed to twocorresponding rigid arms 16 and 17, each defined by a hollow metalsection with a rectangular cross section. Straight portions 7 and 8 maybe connected, for example, by clamps 15 to corresponding tabs 18 fixedto arms 16 and 17.

Arm 16 is connected to rigid portion 13 by a balancing device indicatedas a whole by 20 and for balancing the torque due to the weight of arm16 together with the weight of conduit 5 as a whole. For which purpose,an appendix 21 of a sleeve 19 is fixed to rigid portion 13, so thatsleeve 19 is parallel to rigid portion 13. Sleeve 19 (FIG. 2) comprisesa flat bottom wall 22; and a lateral wall 23 having two diametricallyopposite axial slots 24 and 26. Appendix 21 is welded at slot 24,outwards of wall 23, and has a C-shaped cross section; and the two wingsof appendix 21 are fitted with a pivot 28 defining the axis of rotationof arm 16.

Sleeve 19 is fitted with elastic means for contrasting the torque, withrespect to the axis of pivot 28, due to the weight of arm 16 togetherwith the weight of conduit 5 as a whole. The elastic means may bedefined by any type of contrast spring, e.g. a compression springdefined by a bar of elastomeric material such as polyurethane, or an airor gas, e.g. nitrogen, spring, which may be in the form of a pneumaticcylinder with a piston for compressing the air or gas inside.

In the embodiment shown in FIGS. 1 to 3, the contrast spring is definedby a helical compression spring 29 resting at one end on a guide disk33, and at the other end on a wall 31 closing a container 32 housingspring 29 and itself housed inside sleeve 19.

Arm 16 is connected rigidly to a cam member for controlling thecontrasting action of spring 29 according to the angular position of arm16 about pivot 28. More specifically, the cam member is defined by a cam34 defined by a profiled disk pivoting eccentrically on pivot 28, and ishoused inside the two slots 24 and 26 in sleeve 19. Cam 34 has anappendix 36 fixed rigidly to one end of arm 16, and a shoulder 37 whichcooperates with an edge 38 of appendix 21 to define a stop for thetravel, anticlockwise in FIG. 2, of cam 34.

The outer profile of cam 34 acts on the convex surface of wall 31 ofcontainer 32 to compress spring 29 according to the angular position ofcam 34, and therefore of arm 16, with respect to pivot 28. Slot 26 insleeve 19 allows appendix 36 to rotate to the extent that arm 16 ispositioned substantially horizontally. Two substantially semicircularmembers 39 are fixed, e.g. by screws, to the free edge of sleeve 19 todefine a passage 41 for cam 34, and so lock container 32 inside sleeve19.

Spring 29 is adjusted, i.e. calibrated, to vary the precompression forceof the spring by means of an adjusting member. For which purpose, flatwall 22 of sleeve 19 has a threaded hole 42 engaged by an adjustingscrew 43 which acts on guide disk 33 of spring 29. The precompression ofspring 29 is obviously adjusted before inserting cylinder 32 insidesleeve 19, and is preferably adjusted to balance, at rest, the minimumtorque due to the weight of arm 16 and of conduit 5 as a whole.

Arm 17 is connected to arm 16 by a balancing device 44 for balancing thetorque due to the weight of arm 17, together with the weight of portion8 (FIG. 1) of all-purpose conduit 5 and of hood 6. Balancing device 44is identical to balancing device 20, so the relative component parts areindicated in the drawings using the same reference numbers withsuperscripts, and are described here only briefly. In balancing device44, sleeve 19′ is fixed directly to the end of arm 16, and cam 34′ hasan appendix 36′ fixed in known manner to the end of arm 17.

Pivot 28′ of cam 34′ is carried by two circular plates 40, each having asubstantially tangential appendix 45; plates 40 are held apart by aspacer block 48 located between appendixes 45 to permit rotation of cam34′; and appendixes 45 and block 48 are inserted inside and fixed byscrews to the end of arm 16, so that pivot 28′ of arm 17 is carried bythe end of arm 16.

Compression spring 29′ is located between disk 33′ and a cylindricalblock 49 (FIG. 3) held resting on the profile of cam 34′; the other endof arm 17 (FIG. 1) is connected to hood 6 by a universal joint 46; andhood 6 is fitted with a grip 47 by which it is moved manually withrespect to support 14.

Each of the two balancing devices 20 and 44 in the FIGS. 1-3 embodimentoperates as follows.

Assuming springs 29, 29′ of the two balancing devices 20, 44 arecalibrated to balance the respective minimum torques of arms 16 and 17,displacement of hood 6 by means of grip 47 both in height and alongsupport 14 varies the angular position of arm 16 and/or arm 17, togetherwith that of relative cams 34, 34′, on relative pivots 28, 28′, so thatcam 34 acts on flat wall 31 of relative container 32 to vary thecompression of relative spring 29 according to the angular position ofarm 16 with respect to sleeve 19.

Cam 34′ in turn acts on block 49 to vary the compression of relativespring 29′ according to the angular position of arm 17 with respect toarm 16. In the FIGS. 1-3 embodiment, the action of elastic means 29, 29′is therefore directed radially with respect to the axis of rotation ofrelative arm 16, 17.

In the FIG. 4 embodiment, the action of the elastic means of balancingdevices 20 and 44 is substantially parallel to the axis of rotation ofrelative arm 16, 17. More specifically, balancing device 20 of arm 16comprises an outer sleeve 51 (FIG. 5) having a radial pin 52, which isfixed removably in known manner inside a vertical sleeve 53 having anappendix 54 by which it is fixed to rigid portion 13 (FIG. 4) of conduit5.

A cylinder 56 is inserted inside sleeve 51, and has another radial pin57 which is fixed removably in any known manner to one end of arm 16.Pin 57 is located at a circumferential slot 58 in sleeve 51, so thatcylinder 56 rotates inside, but is axially fixed with respect to, sleeve51. The axis of sleeve 51 therefore represents the axis of rotation ofarm 16, and sleeve 51 acts as a pivot about which arm 16 rotates.

Cylinder 56 has two symmetrical helical cam edges 59 (see also FIG. 6),each of which cooperates with a complementary edge 61 of a correspondingsleeve 62 having the same diameter as cylinder 56. Each sleeve 62 has anaxial slot 63 engaged by a radial pin 64 fixed in known manner to sleeve51 and directed inwards, so that each sleeve 62 slides axially, but isangularly fixed, with respect to sleeve 51.

Sleeves 62 house respective contrast springs acting axially in oppositedirections. More specifically, in the FIGS. 5 and 6 embodiment, eachcontrast spring is defined by a helical compression spring 66 housed ina corresponding cylindrical container 67 in turn housed insidecorresponding sleeve 62. Each container 67 has a flange 68, which restson a second edge 69 of, and perpendicular to the axis of, correspondingsleeve 62.

Container 67 also has an end wall (not shown), on which one end ofspring 66 acts to keep the end wall resting against an end wall ofsleeve 62. The other end of spring 66 rests on a guide disk 71, which,together with container 67 and spring 66, is locked inside correspondingsleeve 62 by a cover 72 fixed by screws to an edge 73 of sleeve 51, sothat springs 66 are coaxial with sleeve 51.

The member for adjusting or calibrating each spring 66 is defined by acorresponding adjusting screw 74, which engages a threaded hole 76 incover 72, and acts on disk 71 to adjust the distance between disk 71 andthe end wall of container 67, and so adjust the precompression force ofspring 66 in the same way as described relative to adjusting screw 43(FIG. 2).

Balancing device 44 between arms 16 and 17 is similar to device 20 inFIG. 5, so the relative component parts are indicated using the samereference numbers with superscripts, and are described here onlybriefly. Sleeve 51′ (FIG. 7) has a radial pin 52′ fixed to the end ofarm 16, and cylinder 56′ has a radial pin 57′ fixed to the end of arm17. In view of the smaller torque to be balanced with respect to device20, cylinder 56′ may advantageously have one cam edge 59′ (see also FIG.8) which cooperates with one sliding sleeve 62′. Provision may thereforebe made for one spring 66′ housed inside sliding sleeve 62′ in the sameway as springs 66 in FIG. 5.

Each of balancing devices 20 and 44 in the FIGS. 5-8 embodiment operatesas follows.

Assuming springs 66, 66′ of the two balancing devices 20, 44 arecalibrated to balance the respective minimum torques of arms 16 and 17,springs 66 and 66′ normally keep respective flanges 68, 68′ ofcontainers 67, 67′ resting on edges 69, 69′ of respective sleeves 62,62′, and manual displacement of hood 6 both in height and along support14 varies the angular position of arm 16 and/or arm 17, together withthat of relative cylinders 56, 56′.

Cam edges 59 of cylinder 56 of device 20 move the two sleeves 62axially, and with them containers 67, to vary the compression ofrelative springs 66 according to the angular position of arm 16 withrespect to sleeve 51; and cam edge 59′ of cylinder 56′ of device 44 inturn axially moves sleeve 62′, and with it container 67′, to vary thecompression of relative spring 66′ according to the angular position ofarm 17 with respect to arm 16.

In a variation of the balancing device, e.g. the one in FIGS. 5 and 6,the two springs 66 are located axially outside the two sleeves 62 (FIG.9), in which is inserted a fixed inner sleeve 77. Each end of sleeve 77is closed by a wall 78 having a threaded hole 79; and each sleeve 62 hasa radial pin 82, which engages a corresponding axial slot 81 in innersleeve 77, so that each sleeve 62 slides axially with respect to, but donot rotate on, inner sleeve 77.

Inner sleeve 77 is fitted with radial pin 52 for connection to verticalsleeve 53 (see also FIG. 4), which engages a radial slot 83 in acylinder 84, in which sleeve 77 is also inserted. Cylinder 84 thereforerotates with respect to, but does not slide axially on, sleeve 77, hastwo cam edges 59 cooperating with two complementary edges 61 of the twosleeves 62, and has an appendix 57 by which it is fixed to the end ofarm 16, so that arm 16 rotates about the axis of inner sleeve 77.

Each spring 66 is located between two guide disks 87 and 88, each havinga central hole. Disk 87 is located outwards, and disk 88 has a flange 89normally held resting on perpendicular edge 69 of sleeve 62. A longadjusting screw 86 extends through the holes in both disks 87, 88, andengages threaded hole 79 in sleeve 77, so that the precompression ofspring 66 is adjusted by adjusting the distance, at rest, between disks87 and 88.

Operation of the FIGS. 9 and 10 balancing device is identical to that ofdevice 20 in FIGS. 5 and 6, and is therefore not described here. Device44 with a single spring 66′ (FIGS. 7 and 8) may also be designed withspring 66′ outside sliding sleeve 62′, and with the fixed sleeve inside.Like the device in FIGS. 9 and 10, the cylinder with the cam edge isalso located on the outside of the inner sleeve to move sliding sleeve62′ axially.

The advantages, as compared with known devices, of the balancing deviceaccording to the invention will be clear from the foregoing description.In particular, the device is extremely compact; springs 29, 29′ and 66,66′ are adjusted by cam members 34, 34′ and 59, 59′, so that themechanism is cheap and easy to produce; and the precompression ofsprings 29, 29′ and 66, 66′ is adjusted easily by means of astraightforward adjusting screw.

Clearly, changes may be made to balancing devices 20, 44 as describedherein without, however, departing from the scope of the accompanyingclaims. For example, the profile of cams 34, 34′ may comprise a lift toachieve optimum balance of the torque of arms 16, 17 in each position;and the cam member may be carried by container 32, as opposed to beingfixed to arm 16, and be carried by block 49, as opposed to being fixedto arm 17.

Moreover, the helical compression spring 29, 29′ may be replaced with anextension spring, which may even be located outside sleeve 19, 19′. Inwhich case, the profile of cam 34, 34′ may comprise a groove engaged bya transmission cable connected to one end of the extension spring. Eachcam edge 59, 59′ may cooperate with a cam-follower member to permit anon-linear edge 59, 59′ for optimum balancing of the torque of arms 16,17 in each position. And arms 16 and 17 may even be balanced by anycombination of the balancing devices described above, with a springacting perpendicular to the axis of rotation of arm 16, 17, as in FIGS.1 to 3, and with a single spring 66′ or pair of springs 66 actingparallel to the axis of rotation.

The straight portions 7 and 8 of conduit 5 may be defined by rigid,smooth pipes; flange 10 of the member supporting rigid portion 13 ofconduit 5 may be wall- or ceiling-mounted, as opposed to being fixed toa bottom support 14, which is normally mounted on a trolley; and thebalancing device may be applied to any arm supporting fixtures to bemoved by hand or motor.

1. A balance assembly comprising: a first arm supporting a first portionof a gas exhaust conduit of a workstation; a second arm supporting asecond portion of the gas exhaust conduit, wherein the first and secondarms are arranged to pivot about an axis of rotation; a first balancingdevice comprising: a first cam member operatively connected with thefirst arm; a first elastic member having a first side connected to afirst fixed element; and a first sliding sleeve cooperating with thefirst elastic member and having a first edge abutting against andsliding over an edge of the first cam member, a second balancing devicecomprising: a second cam member operatively connected with the secondarm; a second elastic member having a first side connected to a secondfixed element; and a block cooperating with the second elastic memberand having a first edge abutting against and sliding over an edge of thesecond cam member, wherein the first and second cams are calibrated tobalance the first and second arms in respective minimum torque angularpositions, and wherein the first cam acts on the first sliding sleeve tovary compression of the first elastic member according to an angularposition of the first arm with respect to the first sliding sleeve, andwherein the second cam acts on the block to vary compression of thesecond elastic member according to an angular position of the second armwith respect to the first arm.
 2. A device as claimed in claim 1,wherein said first or second elastic member comprises at least one barof elastomeric material.
 3. A device as claimed in claim 1, wherein saidfirst or second elastic member comprises at least one air or gas spring.4. A device as claimed in claim 1, wherein said first or second elasticmember comprises at least one helical spring.
 5. A device as claimed inclaim 1, wherein said first or second elastic member is housed in acylindrical container sliding inside said first or second sliding sleevesupporting said axis of rotation; said first or second_cam member beingintegral with a respective one of said first or second arm.
 6. A deviceas claimed in claim 1, wherein the action of said first elastic memberis substantially perpendicular to said axis of rotation; said first cammember being a cam in the form of a disk rotating about said axis ofrotation.
 7. A device as claimed in claim 4, wherein said at least onehelical spring is a compression spring having another end cooperatingwith a guide disk; said compression spring being calibrated.
 8. A deviceas claimed in claim 5, wherein said compression spring has one endresting against a closing wall of said container; said closing wallcooperating with said first cam.
 9. A device as claimed in claim 1wherein said first or second elastic member produces a contrastingaction of compression.